A conventional television receiver, such as a receiver in accordance with NTSC broadcast standards adopted in the United States, Japan and elsewhere, has a 4:3 aspect ratio (the ratio of the width to the height of a displayed image).
Recently, there has been interest in using higher aspect ratios of television receiver systems, such as 2:1, 16:9, or 5:3, since such higher aspect ratios more nearly approximate or equal the aspect ratio of the human eye than does the 4:3 aspect ratio of a conventional television receiver. There has been also interest in using scan conversion of television systems.
Video information signals with a 5:3 aspect ratio have received particular attention since this ratio approximates that of motion picture film, and thus such signals can be transmitted and received without cropping the image information. However, wide aspect television systems which simply transmit signals having an increased aspect ratio as compared to conventional systems are incompatible with conventional aspect ratio receivers. This makes widespread adoption of wide aspect television systems difficult.
It is therefore desirable to have a wide aspect television system which is compatible with conventional television receivers. One such system is disclosed in the U.S. Pat. No. 4,855,824 of J. S. Fuhrer.
FIG. 1 shows again the compatible wide aspect television system disclosed in the U.S. Pat. No. 4,855,824. In FIG. 1, 1201 is an original wide aspect progressive-scan signal with the aspect ratio 16:9 or 5:3. This signal 1201 is comprised of left, right and center panel information and processed so as to develop four separate encoding components 1202, 1205, 1209 and 1210.
The first component 1202 contains time expanded center panel information and time compressed side panel information of low frequency. The second component 1205 contains time expanded side panel information of high frequency. The third component 1209 contains high frequency luminance information. The fourth component 1210 contains vertical temporal helper information of high frequency.
The center panel information in the first component 1202 does not cause a pattern distortion when decoded on a standard television receiver because it has been time expanded. Further, the side panel information of the first component 1202 is multiplexed to the horizontal over-scan regions where such information is hidden from view in a standard television receiver image display.
The side panel information in the second component 1205 is time expanded four times. Therefore, the band of the second component 1205 is compressed to 1/4. As will be described later, the present invention is intended to improve the first and second components 1202 and 1205.
The second component 1205 is processed in an intra-frame averager circuit 1206. A resulting intra-frame average signal output from the intra-frame averager circuit 1206 is converted into a progressive scan format signal. This output is quadrature modulated (frequency shift modulated) with the third component 1209, which has been inter-frame averaged, by a quadrature modulator 1207.
The main signal, i.e., the first component 1202 is also intra-frame averaged in an intra-frame averager circuit 1203. This main signal 1202 is added to a carrier signal from the quadrature modulator 1207 by the adder 1204 and the added output becomes a transmission signal via the quadrature modulator 1208. The reason for summing of the main signal 1202 in the frames is to facilitate separation of the main signal 1202 from the side panel high-pass signal 1205 at the receiving side. Further, the quadrature modulator 1207 reverses carrier phase between lines.
FIG. 2 is a diagram for illustrating the process of intra-frame averaging in the context of the system of FIG. 1. Starting with the block 1301, pairs of pixels 262H apart within a frame, i.e., pixels in different fields of the same field of the first component 1202, are averaged. For example, a pair of original pixels Y1+C1 and Y2+C2 are averaged. The average value, e.g., M1 (M1=[(Y1+C1)+(Y2+C2)]/2) replaces each of the original pixel values. Thus, the pixels in the different fields of the averaged frame, e.g., 1303 have the same value.
The averaged values X1, X3 in the frame 1304 are quadrature modulated in the quadrature modulator 1305 (equivalent to the quadrature modulator 1208 shown in FIG. 2). Thus, the modulated signals in adjacent lines of the same frame 1306 become opposite in phase, as shown by -A1 and A1. The signal 1306 is added to the signal 1303 in the adder 1308. A resulting output signal 1307 becomes M1-A1 in the first field and M1+A1 in the second field.
In a television receiver, the main signal M can be restored by summing the signals in the different fields, while the side panel high-pass component A can be restored by subtracting them.
Next, the construction of the encoder which performs the multiplex signal processing described above and that of the decoder which perform the restoration are explained referring to FIGS. 3 and 4.
FIG. 3 shows the construction of the encoder and 1405 is a terminal to which the main signal 1202 is led. From the signal from the terminal 1405, a signal in the area to which auxiliary signal (the side band high-pass component) is multiplexed by the band-pass filter (BPF) 1406 is extracted. The inter-field sum of this signal in the multiplex area is performed by the intra-frame averager circuit composed of the field delay unit 1408 and the adder 1409. The inter-field sum output from the adder 1409 is progressively scanned by the selector 1412. The output of the selector 1412 is added to a signal outside the multiplex area from the one field delay unit 1411. The signal outside the multiplex area is a signal from the adder 1407 which adds the main signal 1201 to a signal passed through the band-pass filter 1406.
Another input terminal 1401 receives the time expanded side panel high-pass component signal 1205. The inter-field summing of the signal from the terminal 1401 is carried out by the field delay unit 1416 and the adder 1417. The inter-field summed output from the adder 1417 is converted into a progressive-scan format by the field delay unit 1418 and the selector 1419. The progressive-scan format signal is frequency shifted to the multiplex area through the modulator 1420. The phase of the signal shifted to the multiplex area is reversed for every line by the phase reversing circuit 1403 and the selector 1404. This phase reversed output from the selector 1404 is input to the adder 1414 where it is added to the main signal with the side panel signal from the adder 1413 added. The phase reversed output from the selector 1404 is a signal equivalent to the frame signal 1303 shown in FIG. 2.
The auxiliary signal multiplexed output from the adder 1414 is obtained at the output terminal 1415.
FIG. 4 shows the construction of the decoder. The auxiliary signal multiplexed output from the output terminal 1415 is fed to the terminal 1501. The signal from the multiplex area is extracted at the terminal 1501 by the band-pass filter 1502. The inter-field difference and sum calculations are carried out for the signal from the band-pass filter by the field delay unit 1505 and the adders 1506 and 1507. The difference signal encoded from the adder 1506 is the side panel high-pass component of with its phase reversed between the fields.
This signal is demodulated by the demodulator 1508. Thus, the restored output of the side panel high-pass component is obtained at the output terminal 1512. The summed signal output from the adder 1507 is the multiplex area signal of the main signal with the side panel high-pass component removed. This signal is input into the adder 1511 after being processed by the field delay unit 1509 and the selector 1510 and added to the signal outside the multiplex area from the field delay unit 1504. As a result, the main signal with the side panel low-pass component superposed on the horizontal over-scanning area is obtained at the output terminal 1513. Further, the main signal outside the multiplex area is output by the adder 1503 which adds up the output of the band-pass filter 1502 and the signal from the terminal 1501.
According to the system, it is possible to perform the multiplex transmission of auxiliary signals by performing inter-field summing and processing. However, multiplex transmission of auxiliary signals according to this system deteriorates a smooth oblique line into a zigzag line on the image display by the vertical aliasing distortion as shown in FIG. 5.
The phenomenon on the edge is produced because the first field signal is also used in the second field. It is seen that on the encoder shown in FIG. 3, the edge part is made obscure through the inter-field summing by the field delay unit 1408 and the adder 1409 but it cannot be thoroughly improved. Even when a pre-filter (vertical LPF) having a steep frequency characteristic is used instead of the inter-field summing, the zigzag deterioration is caused in accordance with the progressive-scan format conversion.
FIGS. 6(a) through 6(d) illustrate the phenomenon produced at the edge in terms of spectrum. In FIGS. 6(a) through 6(d), the ordinate represents the number of vertical scanning lines and the abscissa represents gains. When the vertical band is limited to 240 lines in advance by a vertical pre-filter, vertical spectra are expressed as shown in FIG. 6(a). The signal having this spectrum produces the folded component as shown in FIG. 6(b) (the output from the adder 1409). If the progressive-scan format conversion is carried out for such a signal at the receiving side, the result would become the same when a vertical interpolating filter shown in FIG. 6(c) was used and the signal obtained from the terminal 1512 or 1513 presents the spectrum shown in FIG. 6(d). In the drawing, the oblique lined section 9001 is left as the folded component, causing notches.
As described above, the system disclosed in the U.S. Patent of J. A. Fuhrer, which performs the inter-field summing and the progressive-scan format conversion had the defect that the zigzag deterioration is caused on the obliques by the aliasing distortion.
Further, conventional scan conversion systems has performed the inter-field summing and the progressive-scan format conversion so that they had the defect of causing the zigzag deterioration on the obliques by the aliasing distortion.